Can-Bus - Electro-Voice Precision P1200RL Owner's Manual

CAN-BUS

Baud Rate
500 kbit/s
250 kbit/s
125 kbit/s
62.5 kbit/s
20 kbit/s
10 kbit/s
CAN-BUS CABLE SPECIFICATIONS
According to the ISO 11898-2 standard, CAN-bus data transfer cabling has to be carried out using
Twisted-Pair cables with or without shielding providing a characteristic impedance of 120Ω. Both ends of
a CAN-bus need to be terminated with 120Ω termination-plugs.
The maximum bus-length depends on the actual data transfer rate, the kind of data transfer cable being
used, as well as the total number of participants on the bus. The following table shows the most essential
coherencies for CAN-networks consisting of up 64 participants:
Cable for data Transmission
Bus Length
Resistance per
Unit Length
0 ... 40 m < 70 mΩ/m
40 ... 300 m < 60 mΩ/m
300 ... 600 m < 40 mΩ/m
600 ... 1000 m < 26 mΩ/m
*
With longer cables and many participants on the CAN-bus, termination resistors with higher impedance than the
Ω
specified 120 are recommended to reduce the ohmic load of the interface drivers and therefore the voltage drop
between the two cable ends.
The following table is meant for first assessment of necessary cable diameters for different bus lengths
and bus-participant numbers:
Bus Length
100 m
250 m
500 m
Additionally, the length of branch lines – for participants that are not directly connected to the CAN-bus
– is also of importance. For data transfer rates of up to 125kbit/s, the maximum length of a single stub
cable should not exceed 2m. For higher bit rates a maximum length of only 0.3m is still permissible. The
entire length of all branch lines should not exceed 30 m.
General Note:
As long as only short distances (up to 10m) are concerned, common RJ-45 patch cables with
100Ω characteristic impedance (AWG 24 / AWG 26) can be used for the cabling inside of a rack-
shelf system. The previously outlined guidelines for network cabling are mandatory as far as the
rack-shelve interconnection or fixed installations are involved.
The CAN-bus allows using different data rates, with the data
Bus Length
rate being indirectly proportional to the bus length. Small net
100 m
works allow baud rates up to 500kbit/s.
250 m For sizable dimensioned networks reducing the baud rate
(minimum 10kbit/s) is necessary. The integration of
500 m
repeaters is generally recommended when the bus-length
1000 m
exceeds 1,000m.
2500 m
5000 m
Cable Diameter
0.25 ... 0.34 mm²
AWG23, AWG22
0.34 ... 0.6 mm²
AWG22, AWG20
0.5 ... 0.6 mm²
AWG20
0.75 ... 0.8 mm²
AWG18
Number of Appliances on the CAN-Bus
32
0.25 mm² bzw. AWG24
0.34 mm² bzw. AWG22
0.75 mm² bzw. AWG18
Termination
124 Ω
127 Ω
*
150 Ω ... 300 Ω
*
150 Ω ... 300 Ω
64
0.34 mm² bzw. AWG22
0.5 mm² bzw. AWG20
0.75 mm² bzw. AWG18
14
Max.
Data Transfer Rate
1000 kbit/s bei 40 m
500 kbit/s bei 100 m
100 kbit/s bei 500 m
62.5 kbit/s bei 1000 m
100
0.34 mm² bzw. AWG22
0.5 mm² bzw. AWG20
1.0 mm² bzw. AWG17